1. Field of the Invention
The invention relates in general to a data driver, and more particularly to a data driver for organic light emitting diode display.
2. Description of the Related Art
Referring to FIG. 1, a driving circuit 100 for a conventional thin film transistor (TFT) liquid crystal display (LCD) panel is shown. The driving circuit 100 includes a horizontal shift register 102, a level shifter 104, a latch 106, a digital-to-analog converter (DAC) 108, and a vertical shift register 110.
The horizontal shift register 102 outputs X horizontal shift control signals HSR(1)˜HSR(X) to respectively control switch set 114(1)˜switch set 114(X), wherein X is a positive integer. The X horizontal shit control signals HSR(1 )˜HSR(X) are sequentially enabled so that the X switch sets 114(1)˜114(X) can be sequentially turned on. Meanwhile, X K-bit pixel data Dt will be sequentially transmitted to corresponding level shifters 104 by the turned-on switch sets 114. Take the first pixel data Dt(1) for example. After receiving the pixel data Dt(1), the level shifter 104(1) will amplify the pixel data Dt(1) and output the amplified pixel data Dt(1) to the latch 106(1). The latch 106(1) will transmit the Dt(1) to the digital-to-analog converter 108(1) for digital-to-analog conversion to generate an analog voltage V(1) accordingly.
The vertical shift register 110 outputs a plurality of vertical shift control signals, VSR(1 )˜VSR(3) for instance. The vertical shit control signals VSR(1 )˜VSR(3) are sequentially enabled so that the analog voltages V(1)˜V(X) outputted by the digital-to-analog converters 108(1)˜108(X) can be sequentially transmitted to their corresponding pixels 112. The brightness of the pixel 112 is related to the analog voltage V received.
By replacing the digital-to-analog converter 108 of the conventional TFT LCD driving circuit illustrated in FIG. 1 with a digital-to-analog current converter which converts digital data into analog currents and replacing the pixel with the current driven type OLED (organic light emitting diode) pixel, a driving circuit for a current driven type TFT-OLED panel can be obtained.
However, the TFT threshold voltage and mobility in different digital-to-analog circuits may not be the same, so that error may occur in the current outputted by the digital-to-analog circuit, resulting in non-uniform brightness across the pixels of the TFT-OLED panel. Therefore, how to reduce the error resulted from the component variation of digital-to-analog circuits has thus become an important issue to be resolved.